The present invention relates to novel methods of sealing alkaline areas of the earth at or beneath the surface, and more particularly to methods of inducing precipitation of carbonates as a means of confining or preventing entry of contaminants, pollutants, sewage or other undesirable leachate waters into groundwaters or aquifers.
Natural subsurface cementation of porous and permeable media below the water table is a well known phenomenon and is one of the key factors in the lithification of sediments, i.e., the filing of small-scale void or pore space between constituent particles or grains by material precipitated or crystallized from solution, or filling of void space (veins, vugs, breccia zones, etc.) in various rocks. Under alkaline conditions (pH&gt;7.5), the most common natural cements by far are calcium or calcium/magnesium carbonates (mainly as calcite--CaCO.sub.3). These natural carbonate cements occur by chemical precipitation or growth from the pore water solution over time and reflect a physiochemical equilibration between mineral constituents of the sediment or bedrock and pore waters, connate waters, or ambient groundwaters.
Deposition of calcium carbonate occurring in nature is a function of temperature, pH, P.sub.CO.sbsb.2, and dissolved calcium concentration, and may be influenced by other constituents in solution. The solubility product (K.sub.sp) of calcite is expressed as a function of calcium and carbonate ion activity (a.sub.Ca ++.times.a.sub.CO.sbsb.3 =K.sub.sp). The actual value of the solubility product is somewhat temperature dependent, and the carbonate ion (CO.sub.3.sup.=) concentration is pH and P.sub.CO.sbsb.2 dependent via the two-stage ionization of carbonic acid to bicarbonate and carbonate ions, viz: EQU CO.sub.2 +H.sub.2 O =H.sub.2 CO.sub.3 K=10.sup.-1.47 @25.degree. C. EQU H.sub.2 CO.sub.3 =H.sup.+ +HCO.sub.3.sup.- K=10.sup.-6.35 EQU HCO.sub.3.sup.- =H.sup.+ +CO.sub.3.sup.= K=10.sup.-10.33
It is a principal object of the present invention to provide a method of sealing surface or subsurface alkaline areas of the earth in a uniformly effective and economical manner.
Another object is to provide a method of sealing cracks, fissures or voids in preselected areas having alkaline conditions utilizing materials having long-term compatibility with host materials.
A further object is to provide novel methods of inducing carbonate precipitation, i.e., growth of a chemical sealant, for permeable zones in alkaline media (bedrock or soils) such as limestone or dolomite.
Still another object is to provide a method of sealing permeable, alkaline areas in a manner providing wider potential dispersion via transport of chemical sealants in aqueous suspensions or solution along groundwater or soil waterflow paths.
A still further object is to provide an improved method of sealing fractures in cement or other alkaline materials, such as marble (metamorphized limestone); in this aspect the invention is useful in repairing cracks in dams or other structures, including cement used to plug natural gas wells, and in marble structures.
Other objects will in part be obvious and will in part appear hereinafter.